This invention relates to a novel improved direct synthesis of Kenyaite-type layered crystalline silicate under hydrothermal conditions from an organic system.
The fundamental unit of crystalline silicate structures is a tetrahedral complex consisting of the Si cation in a tetrahedral coordination with four oxygens. In some structures, the tetrahedra link to form chains which result in fibrous or needlelike morphologies. Single chains result when SiO.sub.4 tetrahedra are joined at two oxygen atoms.
In other silicate structures, the tetrahedra are linked in layers or sheets as in mica minerals. Similar arrangement of the tetrahedra are found in clay minerals wherein two types of sheets may exist, one consisting of aluminum, iron or magnesium ions in a six-fold coordination with oxygens. The layer or sheet structures result from linking between three corners of each tetrahedron to neighboring tetrahedra. Breck, Zeolite Molecular Sieves, John Wiley & Sons, New York, p. 31 (1974) reports that these layer or sheet structures do not have three-dimensional stability and may expand if the layers are forced apart by water, other molecules or ions, and thus, differ from silicates referred to as zeolites which have a framework, three-dimensional structure.
This invention is directed to a novel direct synthesis of Kenyaite-type layered crystalline silicate designated "MCM-25" which is characterized by a unique X-ray diffraction pattern, and to its polymeric chalcogenide intercalcates. Until now, such layered silicates have been found in natural deposts (H. P. Eugster, "Hydrous Sodium Silicate From Lake Magadii, Kenya; Precursors in Bedded Chert", Science, 157, 1177-1180 (1967)) or have been synthesized from inorganic systems (K. Beneke and G. Lagaly, "Kenyaite-Synthesis and Properties", Amer. Minerologist, 68, 818-826 (1983), and copending application for U.S. Pat. Ser. No. 879,787, filed June 27, 1986 now U.S. Pat. No. 4,859,684.